1. Field of the Invention
This invention relates to an axial piston machine utilizing a swashplate design. A cylinder drum is mounted so that it can rotate around an axis of rotation. The cylinder drum is provided with cylinder bores, in each of which a piston is mounted so that it can be displaced longitudinally. The pistons are each supported on a swashplate by a sliding element, such as a sliding shoe.
2. Technical Considerations
On hydrostatic axial piston machines in the form of swashplate machines, the pistons and the cylinder bore form a pressurized cylinder chamber. This results in a piston force which is directed along the longitudinal axis of the piston, which is supported on the swashplate by means of the sliding shoe. A transverse force which generates a torque around the axis of rotation of the axial piston machine is also exerted on a sliding shoe ball-and-socket joint between the piston and the sliding shoe.
On swashplate machines of this type, because the sliding shoe ball-and-socket joint between the piston and the sliding shoe is at a distance from the external support point of the piston in the cylinder bore in the longitudinal direction of the piston, a tipping moment is also applied to the piston. The tipping moment and the transverse force are thereby supported by a force couple that is exerted on the piston and formed by a swashplate-side support force and a cylinder-bore-side support force. The swashplate-side support force is thereby applied to the external support point of the piston in the cylinder bore and thus to the outer end of the guided length of the piston in the cylinder bore. The cylinder-bore-side support force is applied to the inner support point of the piston in the cylinder bore and, thus, on the inner end of the guided length of the piston in the cylinder bore. These support forces increase the friction between the piston and the cylinder bore. As a result of which, the efficiency of the swashplate machine is reduced.
As a result of the tipping moment which is applied to the piston, there is also a gap between the piston and the cylinder bore through which hydraulic fluid flows from the cylinder compartment into the casing. As a result of this gap flow, there is a hydrostatic force which is directed opposite to the transverse force and is applied to the piston in the center of the guided length of the piston in the cylinder bore.
This hydrostatic force simultaneously reduces the swashplate-side support force and increases the cylinder-bore side support force. However, on account of the hydrostatic force that originates from the gap flow, and in particular the resulting increase in the cylinder-bore-side support force, the friction of the axial piston machine is increased, which adversely affects the efficiency of the swashplate machine. The wear to the inner, cylinder-compartment-side end surface of the piston also increases because it is the point at which the cylinder-bore-side support force is applied.
Therefore, it is an object of the invention to provide a hydrostatic axial piston machine of the general type described above which has improved efficiency and reduced wear.